This section provides background information related to the present disclosure that is not necessarily prior art.
Many modern automotive vehicles are equipped with torque transfer systems configured to normally direct drive torque from a powertrain to a set of primary wheels and which can selectively or automatically direct a portion of the drive torque from the powertrain to a set of secondary wheels. Such torque transfer systems, commonly referred to as four-wheel drive or all-wheel drive, can be based on either of a front-wheel drive (FWD) vehicle architecture or a rear-wheel drive (RWD) vehicle architecture. In many vehicles, the torque transfer system operates primarily in a two-wheel drive mode (2WD) for normally driving the primary wheels while the secondary wheels are selectively connected to the powertrain to define a four wheel drive mode (4WD) or an all-wheel drivemode (AWD) only when improved traction is warranted. When operating in the 2WD mode, the secondary wheels are typically disconnected from the powertrain to maximize fuel economy. Various disconnect systems are known for selectively and/or automatically disconnecting the secondary wheels and/or interconnected secondary driveline components in both traditional FWD and RWIF vehicle architectures. For example, commonly owned U.S. Pat. No. 8,165,767 titled “Traction Control System for 4WD/AWD Vehicles”; U.S. Pat. No. 8,313,407 titled “Power Take-Off Unit with Active Coupling and Hypoid Disconnect System”; and U.S. Published Application No. US2011/0275470 titled “AWD Vehicle with Disconnect System” all provide disclosure of disconnect systems and are all incorporated herein in their entirety by reference.
In addition to the need for shifting between the 2WD and 4WD/AWD modes for purposes of improved traction and improved fuel economy, a challenge exists regarding the time needed to switch from the 2WD mode into the 4WD/AWD mode upon detection of conditions warranting enhanced traction control. For example, an undesirable time delay may be required to synchronize and engage the secondary driveline components with the powertrain while the motor vehicle is operating during a wheel slip condition. This is based on the fact that many current torque transfer systems operated based on reaction to detection of a wheel slip condition. Accordingly, a need exists in the art for 4WD/AWD torque transfer systems that are configured and operable to preemptively shift into the 4WD/AWD mode prior to the occurrence of wheel slip. In this regard, it may be beneficial to provide a system operable to estimate the types of road surface and conditions in combination with other vehicular and accessory operating conditions to switch the vehicle into its 4WD/AWD mode prior to the occurrence of wheel slip.